<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>基本选择器</title>
</head>
<body>
<div id="div1">div1</div>
<div class="cls">div2</div>
<div class="cls">div3</div>
</body>
<script src="js/jquery-3.3.1.min.js"></script>
<script>
    //元素选择器  $("元素的名称")
    let div1 = $("div");
    alert(div1.length);

    //id选择器   $("#id的属性值")
    let div2 = $("#div1");
    alert(div2.length);

    //类选择器   $(".class的属性值")
    let cls = $(".cls");
    alert(cls.length);
</script>
</html>